Wiring circuit boards such as TAB (tape automated bonding) tape carrier generally contain a substrate containing an insulating layer and, formed thereon, a wiring pattern containing a conductor layer, and are used in various electronic appliances.
Various electronic parts are mounted on a wiring circuit board and connected to terminal parts of the wiring pattern. The terminals of the electronic parts are made of, e.g., gold. In this case, in order to improve the connectivity of the terminal parts of the wiring pattern with the terminals of such electronic parts, a tin film (tin deposit) is formed so as to coat the terminal parts of the wiring pattern therewith. Herein, the term “connectivity of wiring pattern with electronic part” means the certainty of electrical and physical connection between the wiring pattern and the electronic part. However, there are cases where whiskery crystals called whiskers grow on the tin film on the terminal parts. These whiskers may cause short-circuiting in the wiring pattern.
Patent document 1 discloses that it is possible to inhibit the generation of whiskers for a long period of time by forming a tin-plated layer on a wiring pattern made of copper, followed by subjecting the deposit layer to a heat treatment at 80 to 140° C. However, it is pointed out in patent document 1 that heating at the temperature higher than 140° C. causes a problem, for example, that the tin-plated layer discolors.
Patent document 1: JP-A-2002-124547